Transparent conductive oxide coatings, such as indium tin oxide (ITO), as well as other conductive (e.g., metallic) coatings deposited by magnetron sputtering on unheated substrates are often thermally annealed to improve the functional properties of the material by improving its crystallinity. In the case of ITO, for example, this is done primarily to increase conductivity and to decrease absorption. It will be understood that the term “unheated substrates” are those to which no additional thermal energy is intentionally provided during deposition and include, for example, so-called room temperature depositions. By contrast, however, it is understood that some rise in the temperature of the substrate will occur from physical vapor deposition (PVD) processes such as sputtering.
For the case of coatings on glass and other temperature sensitive substrates, it is often not possible or practical to use radiative, conductive, or convective furnace heating processes commonly used throughout the glass industry for the tempering and/or heat strengthening of glass. In the case of glass, for example, exposures to excessively high temperatures (typically over 600 degrees C.) can lead to significant stress changes in the glass, sometimes even resulting in fracture or deformation. And even at lower temperatures, significant stress changes may occur when exposure times are lengthy. These changes may effectively render the glass unprocessable, e.g., to the point where it can no longer be cut, ground, drilled, or otherwise fabricated into its final physical form.
Conversely, stress changes in the glass are often exploited during tempering and heat strengthening processes, e.g., to improve the mechanical properties of the glass by placing the inner volume of the material under tension and the outer skin under compressive stress. As is known by those skilled in the art, the cost of such processing can be high and sometimes even greater than the cost of the glass itself. Additionally, the glass typically cannot be processed any further following tempering or heat strengthening. Therefore, tempering and heat strengthening processes are typically employed only where required for product functionality and/or safety.
The assignee of the instant application is currently developing a number of products that utilize ITO as a transparent conductive layer. Such products are being developed for use in anticondensation and other applications, e.g., where such low emissivity products are used in residential and/or other applications. When the glass is mounted vertically in these applications, as in the case of a typical window, it is usually not tempered or heat strengthened. Approximately 75-80% of the market by volume falls under this category. Therefore, window manufacturers often are not setup to handle high volume tempering and/or do not wish to bear the additional costs and logistics associated with using tempered glass. Thus, it will be appreciated that delivering an annealed “stock sheet” solution that customers can fabricate into whatever final form they desire would be advantageous to the market adoption of these products. It also will be appreciated that the techniques described herein may be advantageous in other applications where transparent conductive oxide materials are used such as, for example, displays and touch screen products.
In general, it will be appreciated that it would be desirable to provide improved techniques for heat treating coatings in a way that has a reduced impact on the underlying substrate.
Certain example embodiments of this invention relate to a method of making a coated article. A glass substrate is provided. A layer of indium tin oxide is formed, directly or indirectly, on the substrate via physical vapor deposition. The glass substrate with the layer of indium tin oxide thereon is exposed to infrared radiation at a peak emission of 1-2 μm for up to about 108 seconds so as to cause the sheet resistance, emissivity, and absorption to be lower than corresponding values for the as-deposited layer of indium tin oxide. The layer of indium tin oxide is preferentially heated such that the glass substrate does not reach a temperature in excess of about 480 degrees C.
Certain example embodiments of this invention relate to a method of making a coated article. A Glass substrate with a layer of indium tin oxide sputter deposited thereon is provided. The glass substrate with the layer of indium tin oxide thereon is exposed to infrared radiation at a peak emission of 1-2 μm for a time sufficient to cause the sheet resistance, emissivity, and absorption to be lower than corresponding values for the as-deposited layer of indium tin oxide, with the sheet resistance following the exposure to the infrared radiation being substantially the same as the sheet resistance would be if the coated article were heated in a conventional radiant furnace for 3.5 min at 650 degrees C. The layer of indium tin oxide is preferentially heated such that the glass substrate does not reach a temperature in excess of about 425 degrees C.
Certain example embodiments of this invention relate to an infrared heat treatment system configured to heat treat a coated article comprising a glass substrate having a coating physical vapor deposition deposited thereon. An infrared heating element is configured to irradiate infrared radiation at a peak emission of 1-2 μm at the coated article for a predetermined amount of time so as to cause preferential heating of the coating or a portion of the coating such that the glass substrate remains at a temperature below 480 degrees C. without any additional cooling elements. The coating comprises at least one layer of indium tin oxide.
The features, aspects, advantages, and example embodiments described herein may be combined to realize yet further embodiments.